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16 Sep 2005 - 14:45 subtracting integers & absolute value)
Here is how Christopher does this problem:
-1 - ( - 2 )
He pencils in a vertical line across both of the minus signs in the middle, turning them into plus signs: - 1 + ( + 2 ) =
That works for him every time, no matter what the numbers, and he isn't thrown off by the same problem written with an absolute value: -1 - | - 2 | =
This reminds me of Carolyn's belief that you need to get math into a child's hand.
For some reason a problem like: -1 - 2 makes sense to him. He 'sees' that he's adding two negative numbers. Here, too, however, he does a swoop and swoop thing: he squeezes in a plus sign between the 1 and the second minus sign, like this: -1+-2 = Ed's explanation to Christopher that you can think of -1 - 2 as adding two debts -- first you owed 1 dollar, then you borrowed 2 more dollars and you owed 3 -- seems to have been the ticket. I tried that explanation on a friend of mine who is severely math phobic, and she instantly got it, too. Adding debt to debt is something everyone can grasp! It's EVERYDAY MATH FOR THE MASSES!
From one of Carolyn's first posts: That's what the standard algorithms are: they are moves that you learn how to make. Those moves get into your fingers, just like learning the piano or the violin or typing, and eventually you can do them completely mindlessly.
swoop and swoop
the craft of math
subtraction as the difference between 2 numbers
outloud study sheet: subtracting integers & absolute value
notes on integer, subtraction, & absolute value study sheet
Carolyn on introducing absolute value
keywords: integers subtraction addition absolute value opposite add study sheet outloud out loud
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